I'm curious. If the present owner of this TV already has a modern flat-panel set he wants to put on top of the cabinet, what would he need the original TV for?
The only thing I can come up with is that he may want to feed the audio from his home theater setup through the original TV's sound channels, but that doesn't make much if any sense since all home theater receivers have outputs for multiple speakers (some as many as seven, counting subwoofers).
Also, there is the problem of power line isolation. I personally wouldn't try to use a 70-year-old TV with any audio system having solid-state components, unless I were sure beyond the shadow of even the most unreasonable doubt that the isolation capacitors were good--most such caps in unrestored sets of this age all but certainly failed years or decades ago, and cannot be trusted. Even if the original isolation networks were replaced with new components, I would still be leery of such things as ground loops or voltage on the chassis of the modern device.